Biodiesel is an alternative fuel source to petrodiesel, JP-8, and standard gasoline. The use of biodiesel is growing in popularity and market penetration in the United States and worldwide. In general, biodiesel may be defined as a petrodiesel equivalent processed fuel derived from biological sources. Typically, biodiesel is a fuel produced from mono-alkyl esters of long chain fatty acids derived from triglycerides. A “mono-alkyl ester” is the product of the reaction of a straight chain alcohol (e.g., methanol or ethanol) with a triglyceride to form glycerine (also known as glycerin or glycerol) and the esters of long chain fatty acids. The triglycerides are commonly obtained from vegetable oils and animal fats of various origins. Biodiesel has a general formula R′OOCR, where R′ is a straight chain lower alkyl (e.g., C1 to C8) and R is a hydrocarbon chain from C8 to C24.
One method of making biodiesel involves the reaction of triglycerides with methanol and with an alkali alcoholate catalyst. Electrolytic systems have been proposed for use in producing alkali alcoholates from alkali salt and alkali hydroxide solutions. In one example, a sodium-based process is used to make sodium methylate from sodium metal as a raw material. In another example, sodium methylate is made from a sodium amalgam produced from the chlor-alkali electrolysis in a mercury cell by reacting amalgam with alcohol.
Regardless of how the alkali alcoholate is produced, it can be important to measure the concentration of alkali alcoholate product in order to properly control the process for making biodiesel fuel. Although some conventional alkali ion sensors exist, the conventional alkali ion sensors are designed to function based on aqueous electrochemistry. Unfortunately, these conventional alkali ion sensors will not operate correctly with non-aqueous solutions because the aqueous solution present in the reference electrode of the conventional alkali ion sensor mixes with the non-aqueous solution, which changes the reference electrode potential of the conventional alkali ion sensor.